ABSTRACT This project introduces a novel strategy for bioavailability determination of sediment-borne contaminants featuring a wide range of chemical structures, properties and physical-chemical behaviors. The project addresses the pressing need of Superfund stakeholders to determine in a convenient and reliable fashion both human health risks from contaminated sediments and the effectiveness of implemented remediation strategies. The in situ sampling/bioavailability determination (IS2B) tool is a novel, patent-pending device enabling simultaneous determination of contaminant levels in bulk water and pore water at hitherto unattainably low method detection limits (MDLs). When deployed, one half of the tubular IS2B device is buried in sediment and the other is exposed to bulk water. Integrated multi-channel pumps simultaneously draw bulk water and sediment pore water into the active sampling device and push it at, respectively, high and low desirable flow rates through an array of filters and adsorption media. Water samples either can be stored in the device or expelled into the bulk water at will. Due to unlimited access to pore and bulk water during deployment, the IS2B tool provides ultra-low MDLs for a broad spectrum of contaminants, ranging from fully water-soluble to highly sorptive and hydrophobic. This functionality distinguishes the device from presently available passive sampling strategies. Know-how from three previous SRP projects is being leveraged to test the working hypothesis that the IS2B technology can serve to reliably (i) sample bulk and pore water pollutants for analysis in the sub-ng/L range, (ii) inform on the bioavailability and bioactivity of sediment contaminants, (iii) inform on human exposures and associated health risks from fish consumption, and (iv) track the progress of sediment remediation activities. Laboratory and field studies will be conducted with contaminated sediments from Lake Apopka, home to one of Florida's various Superfund sites. To illustrate the breadth of IS2B applicability, this project concentrates on two traditional and three emerging sediment contaminants (p,p'-DDE, dieldrin versus fipronil, triclosan, triclocarban). Because there may be discrepancies between the bioaccumulation predicted via modeling from sampler data and actual bioaccumulation, bioavailability and bioaccumulation of pollutants will be assessed in lab experiments with freshly spiked and long-term aged contaminated sediments via determination of body burdens in two test organisms: Lumbriculus variegatus and Pimephales promelas. Biological responses to contaminant exposure will also be measured in fish using DNA microarray analysis to evaluate effects that may not be predicted solely based on body burden of parent compounds. Mathematical relationships between pollutant concentrations in bulk water, pore water, worms and fish will be formulated from theory and lab data, and applied to IS2B-derived data to predict risk and track the effectiveness of two remediation approaches, granular activated carbon (GAC) amendment and deep tilling of contaminated sediment.